Power modules for ultra-fast wide-bandgap power switching devices

ABSTRACT

Low inductance power modules for ultra-fast wide-bandgap semiconductor power switching devices are disclosed. Conductive tracks define power buses for a switching topology, e.g. comprising GaN E-HEMTs, with power terminals extending from the power buses through the housing to provide a heatsink-to-busbar distance which meets creepage and clearance requirements. Low-profile, low-inductance terminals for gate and source-sense connections extend from contact areas located adjacent each power switching device to provide for a low inductance gate drive loop, for high di/dt switching. The gate driver board is mounted on the low-profile terminals, inside or outside of the housing, with decoupling capacitors provided on the driver board. For paralleled switches, additional terminals, which are referred to as dynamic performance pins, are provided to the power buses. These pins are configured to provide a low inductance path for high-frequency current and balance inductances of the power commutation loops for each switch.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from U.S. provisional patentapplication No. 62/777,357 entitled “POWER MODULE FOR ULTRA-FASTWIDE-BANDGAP POWER SWITCHING DEVICES”, filed Dec. 10, 2018, which isincorporated herein by reference, in its entirety.

TECHNICAL FIELD

This invention relates to power modules for ultra-fast wide-bandgappower switching devices, including power switches comprising GaN HEMTs.

BACKGROUND

High-current power devices, such as single switches and half-bridges,typically require multiple power switching devices to be mounted andinterconnected in parallel within a package referred to as a powermodule. Many forms of power modules are known.

Industry standard power modules with 34 mm and 62 mm rectangularhousings are some of the most widely used for power switches, such ashalf-bridges and single switches, comprising Si IGBTs or SiC MOSFETS.Since introduction of this form of power module over 25 years ago,continual improvements have been made to enhance performance of powermodules, e.g., higher thermal conductivity baseplates, and reduced strayinductance and parasitic resistance, to provide higher efficiency forhigh-frequency switching using SiC MOSFETs. High performance SiCmodules, e.g., full-bridge and half-bridge modules with SiC MOSFETs andSiC Schottky diodes, are now offered by a number of vendors.

For example, standard 62 mm power modules of conventional design arecurrently available for Si IGBT and SiC switching devices in the range600V to 1700V; 20 A to 900 A; with power loop inductance in the rangefrom about 15 nH to 25 nH. To meet creepage and clearance requirementsfor high voltage operation, these modules typically have abusbar-to-heatsink height of about 30 mm, i.e. the housing heightbetween the base of the module and the power terminals. More recently,several companies have offered low-profile 62 mm power module designshaving reduced heights, in the range of about 10 mm to 18 mm, e.g. toprovide more compact power modules, and to provide reduced power loopinductance.

For example, U.S. Pat. No. 9,426,883B2 entitled “Low Profile, HighlyConfigurable, Current Sharing Paralleled Wide Band Gap Power DevicePower Module”, issued 23 Aug. 2016 to McPherson, and U.S. Pat. No.10,136,529 of the same title, issued 20 Nov. 2018, disclose a 62 mm SiCpower module that is about 10 mm in height. A commercially availablepower module of this form comprising a SiC half bridge is reported tohave stray inductance of the power loop of 5 nH between power terminals1 and 3. Although low profile modules offer reduced stray inductance ofthe power loop, a reduced module height necessitates creepage extendersaround the power and control terminals, to meet required creepage andclearance requirements, e.g. for 1200V operation. Many existing powerswitching assemblies and power stacks use a standard heatsink-to-busbarspacing, e.g. 30 mm, and low profile modules cannot be easilyretrofitted into such assemblies.

US2019/0139880A1 by Jakobi et al., entitled “Semiconductor Arrangementwith Reliably Switching Controllable Semiconductor Elements” disclosesan arrangement for a half-bridge module comprising controllablesemiconductor elements having their load paths connected in parallel, toaddress issues relating to uneven distribution of thermal and electricalload amongst the controllable semiconductor elements.

While providing reduced stray inductance in the power loop isbeneficial, another consideration is stray inductance in the gate driveloop, which introduces switching delays. This is particularly importantfor GaN power switching devices, which can operate at higher switchingfrequencies with lower switching losses than SiC MOSFETs. For example,GaN E-HEMTs can operate at switching frequencies in the range from e.g.10 kHz to 2 MHz. Even when operating at lower switching frequencies,since turn-on and turn-off times of GaN E-HEMTs may be only a fewnanoseconds, the fast switching transitions can result in very highdi/dt and dV/dt values (J. Xu et al., “A Performance Comparison of GaNE-HEMTS Versus SiC MOSFETS in Power Switching Applications”, Bodo'sPower Systems, June 2017). Thus, reducing parasitics, such as straypower loop inductance and gate loop inductance, is an importantconsideration for power module design for wide bandgap semiconductorpower switching devices comprising GaN HEMTs. (J. Lu et al., “A HighPower-Density and High Efficiency Insulated Metal Substrate Based GaNHEMT Power Module” Energy Conversion Congress and Exposition (ECCE), pp,3554-3658, 1-5 Oct. 2017). Housing-type power modules designed for IGBTand SiC power switching devices, provide superior thermal performance,are widely available, mature technology and cost effective, but theyhave significant parasitic inductance. Currently available housing-typepower modules are not optimized for use with GaN power switchingdevices, such as high-current GaN E-HEMT half-bridges. These types ofmodules potentially limit performance of ultra-fast GaN switchingdevices.

There is a need for improved or alternative power modules forwide-bandgap semiconductor power switching devices, particularly forapplications using ultra-fast switching devices, such as single switch,half bridge, full bridge and other switch topologies comprising GaNE-HEMTs.

SUMMARY OF INVENTION

The present invention seeks to provide power modules for ultra-fastwide-bandgap semiconductor switches which mitigate or circumvent one ormore of the above-mentioned problems, or at least provides analternative.

Aspects of the invention provide housing-type power modules configuredfor improved performance of wide-bandgap semiconductor switches, e.g.comprising GaN HEMTs. In example embodiments, power modules comprisepower terminals configured to meet creepage and clearance requirements,and at least one of: gate drive terminal members configured for reducedinductance in the gate drive loop; and dynamic performance terminalmembers configured to reduce and balance inductance in the powerpower-commutation loops of parallel-connected switches. Terminal membersmay be arranged to minimized quasi-common source inductance.

A first aspect of the invention provides a power module for awide-bandgap semiconductor power switching device, comprising:

a housing comprising a baseplate and a cover;

a power substrate in thermal contact with the baseplate, a topology ofthe power substrate being configured for mounting thereon of awide-bandgap semiconductor power switching device, the power substratecomprising conductive tracks defining a plurality of power buses andcontrol contact areas for the power switching device;a plurality of power terminal members, each power terminal memberelectrically connected to one of the power buses and extending throughthe cover of the housing to a power terminal;a plurality of terminal members comprising control terminal membersextending from each of the control contact areas; wherein each powerterminal is at a first height h₁ from a base of the baseplate and eachcontrol terminal member extends to a control terminal at second heighth₂ from the base, wherein the second height h₂ is less than the firstheight h₁.

The second height h₂ is selected to provide low-profile controlterminals for low stray inductance of the gate drive loop for each powerswitching device. That is, the control terminals comprise gate andsource-sense terminals for the gate drive loop of each switching device,wherein control contact areas for the gate and source-sense are locatedadjacent each power switching device, and the gate and source-senseterminal members extend directly from said control contact areas, andare configured to provide a low inductance signal path for the gatedrive signal. For example, the low-profile control pins provide ashorter, lower inductance interconnect path to a gate driver boardmounted directly on the gate and source sense pins, below the height ofthe power busbar connected to the power terminals. For example, thestray inductance of the gate loop may be reduced significantly relativeto that of currently available power modules. Reduced stray inductancein the gate loop provides improved performance for operation at higherswitching frequencies, and particularly for operation with ultra-fastswitching devices, such as GaN E-HEMTs, in which turn-on and turn-offswitching transitions are only a few ns, e.g. in the range from 1 ns to10 ns, and which can operate at higher switching frequencies, e.g. in arange e.g. at switching frequencies in the range from >10 kHz to 2 MHz.For example, for high di/dt switching it may be desirable to reduce theparasitic inductance of the gate drive loop to e.g. <30 nH, <20 nH, <10nH or <5 nH.

The first height h₁ is selected to meet required clearance and creepagespecifications, for external power terminals, e.g. a specifiedheatsink-to-busbar distance. The configuration and dimensions of thepower buses and power terminal members provide for a low inductancepower loop.

The height difference (h₁−h₂) provides a space for a driver board to beconnected to the control terminals, i.e. mounted below the height h₁ ofthe power terminals, inside or outside the cover of the housing. Thepower module may comprise a housing wherein the cover comprises a firstportion and a second lower profile portion, wherein the power terminalsextend through the housing at the first height h₁ and the controlterminals extend through the lower profile portion of the housing at thesecond height h₂.

For example, in one embodiment, the cover of the housing comprises a lowprofile portion overlying the power switching devices, e.g. defining arecess or trough in the middle portion of the housing, with controlterminals extending through the cover, so that a gate driver board canbe mounted on the control terminals within the trough, e.g. mounted onthe cover within an area of a footprint of the baseplate of the housing.Decoupling capacitors are mounted on the driver board.

In another embodiment, the height difference (h₁−h₂) provides a spacefor a driver board to be connected to the control terminals and mountedin a space below the height h₁ of the power terminals, and within thecover of the housing. Decoupling capacitors are mounted on the driverboard.

While wide-bandgap switching devices comprising SiC MOSFETS aretypically mounted on the power substrate as bare die, GaN powerswitching devices are typically pre-packaged, e.g. encapsulated in lowinductance packaging. Thus, to accommodate GaN switching devices, thesecond height h₂ provides clearance above the power substrate toaccommodate encapsulated semiconductor power switching devices mountedon the power substrate.

Thus, power modules of example embodiments provide reduced gate loopinductance with arrangement of shorter, “low profile” low-inductancegate and source sense terminal pins, and allow for the driver board tobe directly mounted in close proximity, on or in the housing, whileretaining standard creepage and clearance requirements for powerterminals.

In an embodiment, the power module may have a footprint similar to aconventional power module, e.g. a 62 mm module, which has a generallyrectangular baseplate, having a width and length. The power terminalsmay be placed at each end of the module and low-profile controlterminals are arranged lengthwise along a lower profile middle portionof module, and mounting holes are provided at each end of the module sothat the module can be bolted to an underlying substrate comprising aheatsink.

The topology of the power substrate may be configured for mountingthereon of a power switching device comprising a single wide-bandgappower switching device or a plurality of wide-bandgap power switchingdevices. For example, the power substrate topology may be configured fora single switch, a half-bridge, a full-bridge, or other switch topology.For example, the wide-bandgap semiconductor switching device(s)comprises one of a single switch GaN HEMT, a plurality of a GaN HEMTs, aplurality of GaN HEMTs configured in a half-bridge topology, full-bridgeswitching topology and other well-known switching topologies. For highcurrent applications, multiple GaN HEMTs may be connected in parallelfor each switch position. Thus, another aspect of the invention providesa power module for a wide-bandgap semiconductor switching devicecomprising:

a housing comprising a baseplate and a cover, the baseplate defining afootprint of generally rectangular form comprising ends having a widthand sides having a length;

a power substrate in thermal contact with the baseplate, a topology ofthe power substrate being configured for mounting thereon of a pluralityof wide-bandgap semiconductor power switching devices arranged as firstand second rows extending along a length of the power substrate, thefirst row comprising high-side device positions and the second rowcomprising low-side device positions;the power substrate comprising an arrangement of conductive tracksdefining a plurality of power buses and a plurality of control contactareas for the plurality of semiconductor switching devices, wherein:

-   -   the power buses extend lengthwise adjacent to said first and        second rows of high-side and low-side device positions;    -   first and second rows of control contact areas are arranged        adjacent to the first and second rows of high side and low side        device positions;        a plurality of power terminal members, each power terminal        member extending from one of the power buses on the power        substrate, through a cover of the housing, to a power terminal        at a first height h₁ from a base of the baseplate;        a plurality of terminal members comprising control terminal        members, each control terminal member extending from one of the        control contact areas to a second height h₂ above the base,        wherein h₂ is less than h₁.

The control terminals comprise gate and source-sense terminals for eachpower switching device, and h₂ is selected to provide low-profilecontrol terminals for low stray inductance of a gate drive loop for eachpower switching device. The control contact areas for the gate andsource-sense of each power switching device are located adjacent eachpower switching device and the gate and source-sense terminals extenddirectly from said control contact areas to provide a low inductancesignal path for a gate drive signal. The power terminals are positionedat a height h₁, to meet required creepage and clearance requirements,such as a heatsink-to-busbar distance for high voltage operation, e.g.in a range of 300V to 400V, ≥600V or ≥1200V.

For example, the topology of the power substrate may be configured for asingle switch, half bridge or full bridge switching topology. For ahalf-bridge topology, the first and second rows of device mountingpositions allow for multiple power switching devices to beinterconnected in parallel with low inductance interconnections and theconductive tracks defining the power buses on the power substrate areconfigured to provide low inductance interconnections between the powerterminals and the power switching devices. The control terminals for thegate and source-sense connections for each power switching device areconfigured for low stray inductance in the in the gate drive loop. For afull-bridge topology, the power switching device positions and controlcontact areas are configured accordingly, and the power substratecomprises another power bus connected to a fourth power terminal.

In some embodiments comprising paralleled switches, in addition to thegate drive terminals, i.e. source sense and gate terminal pins, anarrangement of additional terminal members is provided on the powerbuses, for connection to the gate driver board, to provide a lowinductance path for high frequency current, i.e. for high di/dtswitching transients, and to balance inductances in the powercommutation loops of each switch. These additional terminal members arereferred to as dynamic performance terminal members, e.g. dynamicperformance pins.

The baseplate and power substrate may comprise layers of a multilayermetal/ceramic substrate, such as direct copper bonded substrate, whichcan be bolted to an underlying heatsink in a conventional manner, e.g.through mounting holes at each end or at each corner of the baseplate.

For example, in one embodiment, the baseplate topology pattern hasdimensions fitting a standard 62 mm power module pattern having a widthof 62 mm and a length of 107 mm, with M6 mounting holes spaced 48 mm×93m apart. For example, the power terminals extend through end portions ofthe cover at a first height h₁ e.g. in a range from 14 mm to 30 mm andthe second height h₂ of the housing is ≤4 mm. The height differenceh₁−h₂ provides a space to accommodate a driver board mounted on or inthe recess or trough formed by the low-profile middle portion of thehousing.

The low-profile middle portion of the housing allows for a plurality ofshorter, high di/dt terminal pins for the gate drive connections, i.e.comprising gate terminals and source-sense terminals for each switchingdevice, to be arranged along each side of the module, for reduced strayinductance in the gate drive loop, and for improved gate drive phaseequalization to multiple paralleled power switching devices.

Another aspect of the invention provides an assembly of a power modulecomprising at least one power wide-bandgap power switching device with adriver board comprising gate driver circuitry for each power switchingdevice, wherein the gate driver board is mounted on control terminals ofthe power module interconnected with corresponding connectors of thegate driver board. Beneficially, e.g. for improved reliability,decoupling capacitors, such as low profile ceramic capacitors, areprovided on the gate driver board instead of within the power module.

Yet another aspect of the invention provides a power module for awide-bandgap power semiconductor switch comprising:

a housing comprising a baseplate and a cover, the baseplate defining afootprint of generally rectangular form comprising ends having a widthand sides having a length;

a power substrate in thermal contact with the baseplate, a topology ofthe power substrate being configured for mounting thereon of a pluralityof wide-bandgap semiconductor power switching devices arranged as firstand second rows extending along a length of the power substrate, thefirst row comprising high-side device positions and the second rowcomprising low-side device positions;the power substrate comprising an arrangement of conductive tracksdefining a plurality of power buses and a plurality of gate drivecontact areas for the plurality of semiconductor switching devices,wherein:

-   -   the power buses extend lengthwise adjacent to said first and        second rows of high-side and low-side device positions;    -   first and second rows of gate drive contact areas are arranged        adjacent to the first and second rows of high side and low side        device positions;        plurality of power terminal members, each power terminal member        extending from one of the power buses on the power substrate,        through a cover of the housing, to a power terminal at a height        h₁ from a base of the baseplate that meets creepage and        clearance requirements;        a plurality of gate drive terminal members, each gate drive        terminal member extending from one of the gate drive contact        areas through the cover of the housing; and        a plurality of dynamic performance terminal members extending        from the power buses, adjacent each power switching device, the        dynamic performance terminal members being arranged to provide a        low inductance path for high frequency current and balance power        commutation loops of each power switching device.

In some embodiments, the gate drive terminals comprise gate andsource-sense terminals for each power switching device which extend to aheight h₂, which is less than h₁ to provide low-profile terminals forlow stray inductance of the gate drive loop for each power switchingdevice, and the plurality of dynamic performance terminal members extendto height h₂ to provide low-profile terminals for low stray inductanceof the power commutation loop for each switching device.

In another aspect, a power module comprises:

a housing comprising a baseplate and a cover, the baseplate defining afootprint of the power module;

a power substrate in thermal contact with the baseplate, a topology ofthe power substrate being configured for mounting thereon of a pluralityof wide-bandgap semiconductor power switching devices arranged as firstand second rows extending along a length of the power substrate, thefirst row comprising high-side device positions and the second rowcomprising low-side device positions;the power substrate comprising an arrangement of conductive tracksdefining a plurality of power buses, wherein:the power buses extend lengthwise adjacent to said first and second rowsof high-side and low-side device positions;first and second rows of contact areas are arranged adjacent to thefirst and second rows of high side and low side device positions, thecontact areas comprising gate drive contact areas each the plurality ofsemiconductor switching devices;a plurality of power terminal members, each power terminal memberextending from one of the power buses on the power substrate, to a powerterminal at a first height from the baseplate;a plurality of gate drive terminal members, each gate drive terminalmember extending from one of the gate drive contact areas to a secondheight from the baseplate for connection to a gate driver board; anda plurality of dynamic performance terminal members extending from thepower buses, adjacent each power switching device, for connection to thegate driver board, the dynamic performance terminal members having anarrangement that balances inductances of power commutation loops of eachpower switching device and provides a low inductance path for highfrequency current.

Power modules of embodiments described herein are applicable forhigh-speed, wide-bandgap, power switching devices, e.g. using SiC or GaNtechnologies, for switching frequencies ≥10 kHz. Module designs thatoffer reduced stray inductance of the gate drive loops and the powercommutation loops, compared to conventional known housing-type modules,are particularly applicable for ultra-fast power switching devicescomprising GaN HEMTs, in which high di/dt and dV/dt switchingtransitions take place on a ns time scale, and which are capable ofoperating at higher switching frequencies, e.g. in a range from ≥10 kHzto 2 MHz. Power modules of embodiments may be configured to provideseparation of high frequency signal paths of the gate drive loop andlower frequency signal paths of the power loop, to reduce interference.For example, an arrangement of dynamic performance terminals, or“dynamic pins”, provide for distributed power connections from the powerbuses to the driver board, to provide for balancing of power commutationloops of multiple paralleled switching devices. In some embodiments, thepower terminals have a height that meets creepage and clearancerequirements, while the gate drive terminal pins and the dynamicperformance terminal pins are low-profile pins, to provide for lowinductance connections to the driver board. The driver board may bemounted in a low profile trough on the exterior of the housing or withinthe housing, and decoupling capacitors are mounted on the driver board.

Thus, power modules for wide-bandgap semiconductor power switchingdevices are provided for applications using, such as single switch, halfbridge, full bridge and other switch topologies, with particularapplication to ultra-fast wide-bandgap semiconductor power switchingdevices comprising GaN E-HEMTs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (Prior Art) shows a schematic line drawing of an example of anindustry standard power module design;

FIG. 2 (Prior Art) shows a schematic line drawing of an assemblycomprising the power module of FIG. 1, mounted on a substrate, with agate driver board connected to control terminals at one end of themodule, and a busbar fastened to one of the power terminals;

FIG. 3 (Prior Art) shows a schematic line drawing of an example of alow-profile power module and a gate driver board;

FIG. 4 (Prior art) shows a schematic line drawing of a side view of thepower module shown in FIG. 3;

FIG. 5 (Prior art) shows a schematic side view of an assembly comprisinga power module of the type shown in FIGS. 1 and 2, mounted on asubstrate, and a busbar, to illustrate typical dimensions for standardclearance and creepage requirements;

FIG. 6 (Prior art) shows a schematic side view of an assembly comprisinga low-profile power module similar to that shown in FIGS. 3 and 4,mounted on a substrate, with a driver board and busbar;

FIG. 7 shows a schematic diagram of a first view of a power module of afirst embodiment, configured for a half-bridge GaN switch topology;

FIG. 8 shows a schematic diagram of a second view of the power module ofthe first embodiment, showing the exterior form of the housing;

FIG. 9 shows a schematic diagram of a third view of an assembly of thepower module of the first embodiment, with a gate driver board mountedon the housing;

FIG. 10 shows a schematic side view of an assembly comprising the powermodule of the first embodiment with the cover of the housing shown indotted outline;

FIG. 11 shows a schematic side view an assembly comprising the powermodule of the first embodiment with the cover of the housing in place;

FIG. 12 shows a schematic side view of an assembly comprising the powermodule of the FIG. 10, with a gate driver board and a busbar, with theoutline of the cover of the housing indicated by a dashed line;

FIG. 13 shows a schematic side view of an assembly comprising a powermodule of a second embodiment, with a gate driver board and a busbar,with the outline of the cover indicated by a dashed line;

FIG. 14 shows a schematic plan view of the layout of components of thepower module of the first embodiment, as shown FIGS. 7 to 9;

FIG. 15A shows an annoted schematic plan view of components of the powermodule of the first embodiment;

FIG. 15B shows an annoted schematic plan view of components of a powermodule of a third embodiment;

FIG. 16 is a schematic diagram to illustrate current switchingtransients di/dt in a half-bridge circuit using fast GaN switchingdevices for HSS and LLS;

FIG. 17 shows a graphical plot comparing the thermal impedance andparasitic inductance of power modules of various types;

FIG. 18 shows a schematic diagram of an interior view of parts of apower module of a fourth embodiment, configured for a full-bridge GaNswitch topology;

FIG. 19 shows another schematic diagram of an interior view of part ofthe power module of the fourth embodiment, configured for a full-bridgeGaN switch topology, showing the power terminals extending from thepower buses;

FIG. 20 shows a schematic diagram of an assembly of the power module ofthe fourth embodiment with a driver board mounted on the cover of thepower module;

FIG. 21A shows a schematic diagram of an interior view of parts of aprior art power module, configured for a full-bridge GaN switch topologyand FIG. 21B shows a cross sectional view;

FIG. 21C shows a schematic diagram of an interior view of parts of thepower module of the fourth embodiment, configured for a full-bridge GaNswitch topology, as shown in FIG. 19, and FIG. 21D shows a crosssectional view;

FIG. 22A shows a schematic diagram of a view of a power module of afifth embodiment;

FIG. 22B shows a schematic cross-sectional view of an assemblycomprising the power module of the fifth embodiment;

FIG. 23 shows a photograph of an example of a customized power modulecomprising a half-bridge configuration of a plurality of GaN switchingdevices connected in parallel, configured for a low inductance gatedrive loop and with an arrangement of power terminals for balancing ofpower commutation loops;

FIG. 24 shows a photograph of an external view of an example of a DBCpower module type, in the form of an Infineon HybridPACK Drive Module™for a 3-phase inverter;

FIG. 25 shows a photograph of the power module of FIG. 24, with thecover removed to show the layout of internal components and powercommutation lops;

FIG. 26 shows a schematic diagram of a plan view of an example of thelayout of the substrate, switching devices and their interconnectionsfor one phase of the power module of FIG. 25;

FIG. 27 shows a schematic diagram of a plan view of an embodiment of apower module of an embodiment wherein the layout of switching devicesfor one phase of the power module of FIG. 26, is configured with aplurality of dynamic pins connected to power tracks (buses) forbalancing of power commutation loops of parallel connected GaN switchingdevices; and

FIG. 28 shows a schematic diagram for further explanation of thefunction of the dynamic pins in balancing of power commutation loops ofparallel connected GaN switching devices as shown in FIG. 27.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription, taken in conjunction with the accompanying drawings, ofsome embodiments of the invention, which description is by way ofexample only.

DETAILED DESCRIPTION

A schematic line drawing of an example of an industry standard design ofa housing-type power module 10 is shown in FIG. 1. The power module 10has a housing comprising a baseplate 12 and a cover 14, which defines anexterior form of the power module comprising a block of generallyrectangular form, e.g. what is referred to a “62 mm module” havingdimensions of 62 mm×106 mm×30 mm. In this example, three power terminals16 are arranged along the top of the module, and control terminal pins18 are provided at one or both ends of the module. FIG. 2 shows aschematic line drawing of an assembly comprising the power module 10 ofFIG. 1, mounted on a substrate 22, which comprises a cooling module,such as a heatsink or cold-plate with passive or active cooling. Thesubstrate 22 of this type of housing module may be, for example, a DBC(Direct Bonded Copper) substrate, or other thermally conductivesubstrate that provides low thermal impedance. The assembly includes apower busbar 24 fastened to one of the power terminals and a gate driverboard 26 connected to control terminals at one end of the module. Thebusbars 24 run over the top of the module and the driver board 26 ismounted to one side of the module 10, over area 28 of the substrate.

As mentioned above, to meet creepage and clearance requirements for highvoltage operation, modules of this type typically have abusbar-to-heatsink height of about 30 mm, i.e. the housing height hbetween the power terminals and the base of the module, as illustratedschematically in FIG. 2. For example, as illustrated schematically inmore detail in FIG. 5, which shows some typical dimensions of a standard62 mm module 10, the substrate-to-busbar height between substrate 22 andbusbar 24 is ˜30 mm, to meet standard creepage and clearancerequirements, e.g. for 600V or 1200V operation. As illustratedschematically in FIG. 5, the driver board 26 is positioned laterally ofthe module connected to control pins at one end of the power module. Inthis type of module, the control terminals for connection to the gatedriver board are positioned at one end of the module, and also extend toa height of ˜30 mm from the base, so that the gate drive signal from thecontrol terminal terminals is routed laterally from one end of themodule. This arrangement results in a long signal path for the gatedrive, which contributes to stray inductance in the gate drive loop,potentially limiting performance of ultra-fast wide-bandgap switchingdevices, such as GaN HEMTs.

A schematic line drawing of parts of an assembly 30 comprising anexample of a low-profile power module 40 and a driver board 50 is shownin FIG. 3. The power module 40 has a low-profile housing 42, e.g.,having a standard 62 mm footprint similar to that of the module 10 ofFIG. 1. The power module 40 has three large area power terminals 44arranged on the top of the module, and control terminal pins 46 at eachend. The low-profile power contacts 44 are configured to reduce thestray inductance in the power loop, e.g. between the power terminalslabelled + and − in FIG. 3. Since the height of the housing of themodule 40 is ˜10 mm, i.e. significantly lower than the 30 mm height ofthe conventional 62 mm module shown in FIG. 1, the housing 42 comprisescreepage extenders 48 around each of the power terminals 44, and alsoaround the control terminals 46. The driver board 50 has the samefootprint as the underlying power module housing, with sockets formounting on control terminals 46 of the module 40. FIG. 4 shows aschematic side view of the power module of FIG. 3 to illustrate typicaldimensions, e.g. the housing 42 and the power terminals 44 have a heightof about 10 mm, and the control terminals extend to a height of about 17mm. As shown schematically in FIG. 6, the driver board 50, with driverboard components 56, can be mounted directly over the module 40, e.g. asillustrated, overlying a power busbar 54 which is connected to one ofthe underlying power terminals of the module 40. This low profile designis configured to offer low stray inductance in the power loop, e.g. ˜5nH. However, as explained in the above referenced U.S. Pat. No.9,426,883, the gate loop connections to the power switching devices aremade from the control terminal pins 46 via an interconnection boardcarrying gate connections and kelvin source (source-sense) connections.The interconnection board is separate from and lies above the powersubstrate carrying the power buses and the switching devices, routingthe gate drive signal laterally from the control terminal pins 46 whichextend from the top of the module. This arrangement contributes to strayinductance in the gate drive loop, potentially limiting performance ofultra-fast wide-bandgap switching devices. For example, effects ofparasitic inductances for a half-bridge power stage comprising twohigh-side and two low-side GaN HEMTs in parallel has been discussed indetail in the above-referenced article by J. Lu et al., entitled “A HighPower-density and High Efficiency Insulated Metal Substrate Based GaNHEMT Power Module” (ECCE 2017), and references cited therein, and in apresentation by J. Lu et al. entitled “Parasitics Optimization for GaNHEMTs in Conventional Housing Type Power Modules”, PCIM 2019, 4-9 May2019. These references discuss the effects of commutation loopinductance, gate-drive loop inductance, mutual inductance between thepower loop and gate loop, and quasi-common source inductance withrespect to an insulated metal substrate (IMS) half-bridge power module;and these references are incorporated herein by reference in theirentirety.

From these analyses, it is apparent that for conventional housing typepower modules such as the example illustrated in FIGS. 1 and 2 (PriorArt), a housing having a housing height that meets the creepage andclearance requirements for high voltage operation results in highparasitic inductances of the gate drive loop and the power commutationloop. A low profile housing power module, such as the exampleillustrated in FIGS. 3 and 4, reduces parasitic inductance in the powerloop, but may violate the creepage and clearance requirements for somepower electronics systems.

Housing type power modules of some illustrative embodiments are nowdescribed, by way of example, in which the power terminals are providedhaving a first height to meet creepage and clearance requirements, andgate driver terminals and dynamic performance terminals, are low profileterminals of a second height, which is lower than the first height, toprovide reduced parasitic inductances in the gate drive loop and in thepower commutation loop.

A schematic diagram of a first view of an assembly of parts of a powermodule 100 of a first embodiment, configured for a half-bridge GaNswitch topology is shown in FIG. 7. A housing of the module 100comprises a baseplate 120, defining a footprint of generally rectangularform, and a cover 110. The cover 110 is represented schematically as asemi-transparent element to show the inner components of the assembly.The baseplate 120 is a thermally conductive layer that supports a powersubstrate 122, e.g. a thermally conductive, electrically isolating,ceramic layer on which is defined a plurality conductive metal tracksdefining power buses 124-1, 124-2 and 124-3 and a plurality of contactareas 123 for terminal members, i.e. pins or blades 134, 136 and 138. Aplurality of GaN power switching devices 130 and 132 are mounted on thepower substrate 122. The GaN power switches 130 are arranged in a firstrow comprising 8 high-side switch (HSS) positions of the half-bridge,and GaN power switches 132 are arranged in a second row comprising 8low-side switch (LSS) positions of the half-bridge, and the 8 HSS andLSS are connected in parallel. The thermally conductive baseplate 120provides mechanical support for the module and may comprises asingle-layer or multi-layer structure, e.g. a thermally conductive metalsubstrate, such as copper, or a multi-layer thermally conductivemetal-ceramic substrate, such as DBC, and typically has an arrangementof mounting holes (not shown in FIG. 7) for bolting the module to asubstrate comprising a cooling module, e.g. a heatsink with passive oractive cooling.

The conductive tracks of the power substrate define first and secondpower buses 124-1 and 124-2 extending lengthwise along first and secondsides of the power substrate, adjacent the low-side and high-side powerswitching devices 130 and 1302. First and second power terminal members125 are bonded to, and form an electrical connection with respectivefirst and second power buses 124-1 and 124-2 at one end of the powersubstrate, and extend upwards through the cover 110 of the housing toexternal power terminals 126-1 and 126-2. The third power bus 124-3extends between rows of high side and low side device positions to athird power terminal member 127. The third power terminal member 127 isbonded to, and forms an electrical connection with the third power bus124-3, and extends through the cover 110 of the housing to externalpower terminal 128 at the other end of the power substrate. Conductivetracks of the power substrate also define an arrangement of contactareas 123 for first and second rows of terminals 134, 136, and terminals138 in the middle. The first and second rows of terminals 134, 136 arearranged adjacent the first and second rows of high side and low sideswitching devices 130 and 132, and other terminals 138 are providedbetween the first and second rows of high-side and low-side switchingdevices 130, 132. These terminals include terminal members, e.g. in theform of pins, which provide gate G and source-sense SS connections foreach of the high-side and low-side switching devices. Additionalterminal members, that are referred to as “dynamic performanceterminals” or “dynamic pins” 140-P and 140-N are also provided to eachof the first and second power buses. The function of dynamic pins 140-Pand 140-N will be described in detail with reference to FIGS. 14, 15A,15B and 16. As illustrated schematically in FIG. 7, the terminal membersor pins 134, 136, 138 are bonded to gate drive contact areas 123 foreach switching device, and extend to a height of a few mm above thepower substrate, below the height of the power terminals 126 and 128.The gate G and source-sense SS control terminals are located in closeproximity, i.e. adjacent, to each switching device, and provide short,low inductance control terminal interconnections for the gate drivecontrol loop for each switching device. The terminals may also includeterminals for sensors such as a temperature sensor.

Switching devices comprising Si IGBTs and SiC MOSFETs may be provided asbare die. In contrast, GaN power switching devices are typicallypre-packaged, e.g. each GaN E-HEMT die is embedded or encapsulated in alow inductance package, with source, drain and gate contact pads. Thepackage may comprise, for example, GaN Systems Inc. GaNPx™ type ofembedded packaging. For example, as illustrated schematically in FIG. 7,each packaged GaN device 130, 132 provides source, drain and gatecontact areas on a top side of the package, and has a thermal pad on theother side, for attachment of the GaN package to the power substrate122, in thermal contact with the power substrate. In this example, thesource and drain contact pads of each package are interconnected torespective power buses by interconnects comprising multiple wirebonds.Gate connections G and source-sense connections SS to respectiveterminals are also provided by wirebonds.

The exterior form of the cover 110 of the housing is shown schematicallyin FIG. 8. The cover 110 has end portions 142 and 143 of a first height,e.g. >14 mm, and a lower-profile middle portion 144 of a second height,the second height being less than the first height, e.g. ≤4 mm, so thatthe middle portion forms a recess, or trough 146, for mounting thereonof a gate driver board.

As shown in the schematic view of the assembly 101 in FIG. 9, the firstand second power terminal members 125 each extend from the respectivepower buses 124-1 and 124-2, through the cover of the housing to firstand second external power terminals 126 on top of one end portion 142 ofthe housing; the third power terminal member 127 extends through thecover of the housing to a third external power terminal 128 on top ofthe opposite end 143 of the housing. The pins or blades of the rows ofterminals 134 and 136 extend through the low-profile middle part 146 ofthe housing along each side of the housing for interconnection tocorresponding connectors of the overlying driver board 150. The pins orblades of terminals 138 extend through a middle portion 144 of the coverfor interconnection to corresponding connectors of the overlying driverboard 150. Thus, as shown schematically in FIG. 9, control terminals134, 136, 138 extend through the surface 152 of the driver board anddecoupling capacitors 154 are mounted on the surface 152 of the driverboard 150.

FIG. 10 shows a schematic side view 100-1 of an assembly comprising thepower module of the first embodiment, with the outline of the cover 110of the housing shown by a dashed line. The baseplate 120 of the powermodule 100 is thermally conductive and is mounted in thermal contactwith the substrate 112, which comprises a heatsink. The power substrate122 is in thermal contact with the baseplate 120, and power terminalmembers 125 and 127 extend upwards from conductive tracks defining powerbuses on the power substrate 122 to external terminals 126 and 128 ontop of the housing cover 110, at a height h₁. The terminal members orpins 134 and 136 extend through the low-profile part 146 of the housing,that forms a recess or trough in the top of the cover 110. The terminalpins 134 and 136 extend to a height h₂, which is less than h₁. Theposition of the plurality of GaN power switches 130 and 132 on the powersubstrate 122 is also indicated schematically. Since the GaN powerswitches are encapsulated (whereas Si IGBTs and SiC MOSFETS are usuallyprovided as bare die) the clearance between the power substrate 122 andthe cover 110 of the housing in the region of the trough 146, provides aspace for mounting of the encapsulated GaN devices, and for wirebondedconnections of the source, drain and gate pads of the encapsulated GaNdevices, as appropriate, to power buses and contact areas for thecontrol terminals. For example, this clearance is several mm, and thelow profile part of the housing may be e.g. 4 mm or less in height. Theconfiguration and height h₂ of terminal pins G and SS for the gate andsource-sense connections are selected to provide short, low-profileterminals which reduce the stray inductance in the gate drive loop e.g.h₂ is ˜5 mm, and preferably less than 10 mm. The height h₁ of the powerterminals 126 and 128 is selected to provide a heatsink-to-busbardistance that meets required creepage and clearance requirements, e.g.for an operational voltage of >600V.

FIG. 11 shows a schematic side view 100-2 of the assembly of FIG. 10,comprising the power module of the first embodiment with the cover 110of the housing in place, showing external power terminals 126 and 128 onthe exterior of the cover 110 at height h₂ and low-profile terminalmembers 134, 136 and 138 extending through the cover of the housing atheight h₂, within the trough or recess created by the low-profile partof the cover 110.

FIG. 12 shows a schematic view 100-3 of an assembly comprising the powermodule of FIG. 10, with the outline of the cover 110 of the housingindicated by a dashed line. The assembly comprises baseplate 120, powersubstrate 122, GaN switching devices 130, power terminal members 125 and127 extending through the cover 110 of the housing to external powerterminals 126 and 128 at height h₁, and terminals 134 extending throughthe cover 110 at height h₂. A gate driver board 150 is mounted oncontrol terminals 134, within the trough 146 on top of the housing cover110. Also shown is positioning of busbars 156 overlying the gate driverboard 150, for connection to the external power terminals 126 and 128.To accommodate decoupling capacitors 154 on the driver board 150, belowheight h₁, low-profile ceramic capacitors may be preferred. If thedriver board and its components extend above the height of the powerterminals, the busbar 156 may be routed accordingly, e.g. above oraround the driver board and its components.

The schematic view in FIG. 13 shows an assembly 200 comprisingcomponents of a power module of a second embodiment, comprising abaseplate 220, power substrate 222, power terminals 225 and 227extending through the cover 210 of the housing to external powerterminals 226 and 228 on top of the housing at height h₁, and lowprofile control terminals 234 extending to height h₂, all of which aresimilar to those shown in FIG. 12, except that, in the assembly of thisembodiment, the driver board 250, with its components, is containedwithin the cover 210 of the housing, underlying the busbar 256.

FIG. 14 shows a schematic plan view of the substrate 122 showing thelayout of components of the power module of the first embodiment, whichis illustrated schematically in FIGS. 7 to 9. There are a plurality ofGaN HEMT switching devices, comprising HSS 130 and LSS 132.interconnected in parallel in a half-bridge configuration. As mentionedabove, to reduce the gate loop inductance for each HSS and LSS, lowprofile terminal pins for source sense SS and gate G connections areplaced in close proximity to each GaN HEMT, i.e. terminals 136SS and136G for the LSS and 138SS and 136G for the HSS. The first row ofterminal pins 134 comprises multiple additional pin 140-P arranged alongthe V+ power bus 124-2. The second row of terminal pins 136 comprisesmultiple additional pins 140-N arranged along the V− power bus 124-1.The additional pins 140-P and 140-N are configured to provide a lowinductance, and low resistance, signal path for high di/dt transientsfor each of the HSS and LSS switches which are connected in parallel,and will be referred to as dynamic performance pins or “dynamic pins”.Thus, as illustrated schematically in FIG. 15A, as annotated by reddotted arrows, the dynamic pins provide a more balanced powercommutation loop inductance for each of the HSS and LSS switches whichare connected in parallel. As illustrated schematically in FIG. 15B, ina module of a third embodiment, when the dynamic pins are omitted,although this topology provides low inductance SS and G terminal pins inclose proximity to each GaN switching device for reduced gate loopinductance for each HSS/LSS switch, without the dynamic pins, there areunbalanced power commutation loop inductances for each parallelconnected HSS/LSS.

FIG. 16 is a schematic diagram to illustrate current switchingtransients di/dt in a half-bridge circuit using fast GaN switchingdevices for HSS and LLS. When either the HSS or LLS is on, current willflow through the respective power buses, as indicated by thick bluearrows. Since GaN HEMTs have turn-on and turn-off times of a few ns,during turn-on and turn-off, each switch will experience high di/dttransients, as indicated schematically in red in FIG. 16. When there aremultiple GaN switches connected in parallel, each has a powercommutation loop inductance, which may differ based on layout, e.g. asshown in FIGS. 15A and 15B. An arrangement of multiple dynamic pins foreach HSS/LSS GaN switch provides a low inductance path, as illustratedschematically in FIG. 15A, between each power bus and the driver board,which balances, or at least reduces imbalances, in the inductance ofeach power commutation loop, for dissipation of high di/dt transients,to provide improved performance, e.g. reduce oscillations andinstabilities.

Thus, a power module comprising a GaN HEMT half bridge topologycomprising a plurality of parallel connected GaN HSS/LSS switches, ofthe embodiment illustrated schematically in FIGS. 7 to 14, and FIGS. 15Aand 15B, provides two solutions to address parasitics and improveperformance of housing-type power modules for wide-bandgap semiconductorswitches. Firstly, the physical design of the power module provides ahousing with a low-profile central portion with low inductance terminalsfor mounting of the driver board, and end portions provide powerterminals at a height that meets creepage and clearance requirements.The low profile portion may be a recess or trough which accepts thedriver board. This allows for low-profile, i.e. shorter, lowerinductance, lower resistance control terminal members, e.g. source-senseSS and gate G pin in close proximity to each GaN switch, to reduce thegate loop inductance, i.e. for low stray inductance of a gate drive loopfor each GaN power switching element. Secondly, provision of rows ofmultiple dynamic pins arranged to connect the power buses to the driverboard provides a low inductance path for high di/dt switching transientsto balance the inductance of power commutation loops for each of theparalleled GaN power switching elements.

A graphical comparison of the performance of various types of powermodules is illustrated schematically in FIG. 17. This plot shows theparasitic inductance vs. thermal impedance for four conventional typesof power modules and a power module of the first embodiment, which isreferred to as a U-type module. A GaN power switch in a GaNPx typeembedded package provides very low parasitic inductance, but has ahigher thermal impedance, and is e.g. suitable for power applications,such as ≤1 kW. Insulated Metal Substrate (IMS) modules can provideexcellent thermal performance for high power applications, e.g. up to 30kW, with low parasitic inductance, at reasonable cost. Low profilemodules, such as illustrated by the example shown in FIGS. 3 and 4,provide reduced power loop inductance, but may not meet standardcreepage and clearance requirements for high voltage operation. Housingtype power modules, e.g. as illustrated by the example shown in FIGS. 1and 2, have low thermal impedance, i.e. superior heat dissipation forhigh power applications, but have high parasitic inductances, whichlimits performance of fast GaN switching devices. A U-type module, forexample, as illustrated by the module first embodiment described above,provides a housing module design with reduced parasitics, i.e. reducedgate loop inductance and reduced and more balanced power commutationloop inductances, for improved performance, and low thermal impedance.

FIG. 18 shows a schematic diagram of an interior view of an assembly 300of components of a power module of a fourth embodiment, configured for afull-bridge GaN switch topology. The assembly 300 comprises a thermallyconductive baseplate 320 having bolt holes 321 for mounting to anunderlying cold plate or heatsink. For example, the baseplate comprisesa thermally conductive metal layer or a thermally conductivemetal-ceramic multilayer substrate. A power substrate 310 is provided onthe baseplate 320. The power substrate comprises e.g. a ceramicsubstrate and a metal layer defining conductive metal tracks for powerbuses 324-1, 324-2, 324-3 and 324-3 and contact areas 323 for rows ofterminals 334, 336 and 338. The baseplate 320 and power substrate 310may be separate elements, or they may be provided by layers of amultilayer substrate, such as a direct bond copper (DBC) substrate.Device areas of the power substrate are arranged for attachment ofencapsulated GaN power switching devices 500 arranged in two rows, i.e.a first row of high side switches 500-1 and a second row of low-sideswitches 500-2. Each switch position comprises two GaN E-HEMTS connectedin parallel. The GaN E-HEMTs are packaged, e.g. encapsulated inpackaging comprising low inductance interconnections to source, drainand gate contact areas on a top side of the package as illustratedschematically, and a thermal pad on the underside of the package. Thepower buses 324-1, 324-2, 324-3 and 324-4 extend between the rows of GaNpower switching devices, with areas for attachment of power terminalmembers. Terminal members 334 and 336, i.e. gate terminals G andsource-sense terminals S for each GaN switching device are arranged asrows extending lengthwise along each side of the power substrate 322,and extend directly from control contact areas 323 placed in closeproximity to the respective GaN device that they control. Thelow-profile terminals 334 and 336 for the gate G and source-sense SSconnections for each device are bonded to and electrically connected tothe control contact areas 323 to provide a short low inductance gatedrive control connection. The control terminals may comprise additionalterminal members 338 for other elements, e.g. for a temperature sensor.

FIG. 19 shows another (rotated) schematic diagram of an interior view ofthe assembly of parts the power module of the fourth embodiment shown inFIG. 14, and further comprising power terminal members 325 and 327bonded and electrically connected to each of the power busses 324-1,324-2, 324-3 and 324-4. The power terminal members 325 and 327 extendupwardly from the power busses to external power terminals 326 and 328at a first height h₁ above the baseplate, to meet required creepage andclearance specifications, such as a minimum substrate-to-busbar height.The control terminals 334 and 336 extend to a second height h₂, lessthan h₁, to provide low-profile, low inductance control terminals forthe gate drive connections.

FIG. 20 shows a schematic diagram of an assembly of the power module ofthe fourth embodiment, with the cover 310 of the housing in place andwith a driver board 350 mounted on the control terminals in the recessof the cover 310 of the power module 300. This arrangement with directconnection of the gate driver board to the low-profile control terminalsprovides for a shorter gate drive loop, to provide reduced strayinductance in the gate loop circuit compared to conventional powermodules. By way of example, the height of the housing in the recess maybe 4 mm or less, and the control terminal members extend directly fromthe control contact areas adjacent each GaN device, through the cover inthe recess to ends of the terminals at height h₂, which may be e.g. ˜5mm. Thus, the configuration of the low-profile gate drive terminals ofthe embodiment shown in FIG. 15 significantly reduces stray inductancein the gate drive loop compared to conventional forms of power modules.For example, for the prior art module shown in FIG. 1 the control pinsextend 30 mm above the base. For the low-profile module shown in FIG. 3,the control pins extend, above the power terminals, to 17 mm and thearrangement of the control pins at one end of the module results in alonger signal path for the gate drive loop, through a gate and sourceboard, which adds parasitic inductance in the gate drive circuit.

Reduced stray inductance in the gate loop provides improved performancefor operation at higher switching frequencies, and particularly foroperation with ultra-fast switching devices, such as GaN E-HEMTs, inwhich turn-on and turn-off times for switching transitions are only afew ns, e.g. in the range from 1 ns to 10 ns, and which can operate athigher switching frequencies, e.g. at switching frequencies in the rangefrom >10 kHz to 2 MHz. For example, while not wishing to be limited to aspecific values of stray inductance, for high di/dt switching it may bedesirable to reduce the parasitic inductance of the gate drive loop by10 nH or 20 nH relative to currently available power modules, forexample, to provide a stray inductance of the gate loop in a range suchas <30 nH, <20 nH, <10 nH or more preferably <5 nH.

For example, simulations may show that it is required to reduce the gatedrive loop inductance to ≤10 nH to avoid false-triggering oroscillation. For a power module of the embodiment shown in FIGS. 7 to 12and 14, based finite element modeling simulation, with the proposedhousing and terminal configuration, the gate driver loop inductance canbe controlled to be <5 nH, and power commutation loop inductance can bereduced to ˜2 nH. The presence of two rows of dynamic performanceterminals provides a more symmetric arrangement and reduces thequasi-common source inductance to ˜0.3 nH (J. Lu et al. “ParasiticsOptimization for GaN HEMTs in Conventional Housing Type Power Modules”,PCIM 2019, 4-9 May 2019).

In variants of the assembly of the power module of the embodiment shownin FIG. 20, the gate driver board may be configured to fit within thefootprint of the baseplate, below height h₁ of the power terminals (e.g.similar to the arrangement shown in FIG. 12), and/or the cover and gatedriver board may be configured so that the gate driver board is mountedwithin the cover of the housing (e.g. similar to the configuration shownin FIG. 13).

FIG. 21C shows a schematic diagram of an interior view of parts of thepower module of the fourth embodiment, i.e. as shown in FIG. 19,configured for a full-bridge GaN switch topology and FIG. 21D shows aschematic cross-sectional view. For comparison, FIG. 21A shows aschematic diagram of an interior view of parts of a prior art powermodule, configured for a full-bridge GaN switch topology and FIG. 21Bshows a schematic cross-sectional view.

FIG. 22A shows a schematic diagram of a view of a power module 400 of afifth embodiment, wherein the housing 401 comprises a baseplate 420 andcover 410, in which four power terminals 426 are arranged along a top ofthe cover 410 of the module, and a row of control terminals 434 extendthrough a low-profile part 411 of the cover 410, for mounting of adriver board thereon, i.e. extending laterally of the cover 410 ofhousing. FIG. 22B shows a schematic side view of the power module 400 ofthe fifth embodiment showing the power terminals 426 extending throughthe top of the housing cover 410 at height h₁ and the low profilecontrol terminals 434 at height h₂. This alternative configurationprovides for height h₁ of the power terminals to be selected to meetcreepage and clearance requirements, and for height h₂ to provide lowprofile control terminals for lower inductance in the gate drivecircuit, for mounting of the gate driver board on the control terminals,with the gate driver board extending laterally of the housing.

Advantageously, power modules in which power terminals extend througheach end of the cover of the housing to height h₁, and a middle portionof the cover of the housing is recessed, e.g. to form a trough, enablesmounting of the gate driver board on top of the lower profile part ofthe housing, for example as illustrated schematically in FIG. 12, withthe gate driver board interconnected to the underlying controlterminals. Alternatively, the gate driver board can be connected to thecontrol terminals within the housing, for example, as illustratedschematically in FIG. 13.

Referring back to FIG. 19, the interconnections of the power module forthe gate and source-sense for each power switching device 500-1 and500-2 are configured to reduce the inductance in the gate control loop,e.g. the low profile control terminals are low inductance terminalmembers located in close proximity, i.e. adjacent each switching device,to provide a short interconnect distance to the gate driver controlboard which is mounted directly on the control terminals. Thisarrangement of low-profile, short low inductance gate and source-senseconnections for each switching device reduces the stray inductance ofthe gate loop circuit compared to conventional power module designs.This configuration also provides for separation of high frequency di/dtsignal paths of the gate drive loop, and lower frequency signal pathsbetween the power terminals of the power loop. This separation of thehigh frequency signal paths in the low inductance gate driver controlloop from lower frequency signals of the low inductance power loop,reduces interference. Also, for example, this arrangement allows for DCterminals on one end of the power module and AC terminals on the otherend of the power module. This design configuration overcomesdisadvantages of known power module designs that have long gate controlconnections extending lengthwise between the control terminals on thepower substrate, e.g. routed through conductive tracks on a separategate connection board, to external connections to the gate driver board.

Although not illustrated in FIGS. 18 to 20, where multiple GaN HEMTswitching devices are connected in parallel in a full bridgeconfiguration, each HSS/LLS switch may be provided with a plurality ofdynamic pins, e.g. as described above with reference to the GaN HEMThalf bridge of the first embodiment, for connection to the driver board,to provide a low inductance path for high di/dt transients. That is, inFIGS. 18 and 19, the rows of terminal pins 334 and 336 include only theterminal pins for SS and G connections. The rows of terminal pins 334and 336 may be extended to provide a plurality of dynamic pins to thepower buses, adjacent each switching device, similar to the dynamic pins140 of the power module of the first embodiment shown in FIGS. 7, 9, 14and 15A.

In conventional power modules, decoupling capacitors are providedinternally in the power module, but this means they are closer to theheat source. For improved reliability, the decoupling capacitors areprovided on the driver board, e.g. as shown schematically in FIG. 9.

In the structures of the embodiments described above, the baseplate andpower substrate are described as separate layers or elements, but theymay be integrated, e.g. comprise layers of a multi-layer substrate,comprising thermally conductive and electrically insulating layers andelectrically conductive layers. For example, the baseplate and powersubstrate may comprise a DBC (Direct Bond Copper) substrate. Forexample, a DBC substrate may comprise a thick copper baseplate, anelectrically insulating layer of a thermally conductive ceramic, such asalumina or aluminum nitride, and an electrically conductive layer ofcopper providing the conductive metal layer defining power buses andcontrol contact areas of the power substrate. The baseplate has a highthermal conductivity and is ideally CTE matched to layers of the powersubstrate. Power modules of embodiments that are disclosed herein areconfigured for high-current, high-speed power switching devices, such asGaN HEMTs. In some embodiments, the housing has a low-profile middleportion providing a trough for mounting thereon of a driver board. Powercontacts are provided on end portions of the housing, which have aheight greater than the middle portion, to provide a heatsink-to-busbardistance which meets conventional/standard creepage and clearancerequirements, e.g. for 300V to 400V operation, such as 380V forindustrial motors and 400V for electric vehicles, or for otherapplications requiring higher voltage operation, e.g. >600V or ≥1200 Lowprofile control terminals for gate and source-sense connections compriserows of short pins or blades extending along each side of thelow-profile middle portion of the housing, from control contact areas inclose proximity, i.e. adjacent to, each of the power switching devices.Additional low profile dynamic performance pins are arranged along thelength of each side of the low-profile middle portion of the housing toprovide distributed low inductance pathways, for high di/dt switchingtransients in power commutation loop, between the power buses and thedriver board, thus balancing, or at least reducing imbalances, in theinductances of the power commutation loops for multiple parallelconnected GaN LSS/HSS switching devices, e.g. for improved dynamicperformance. The gate driver board is mounted on the low profile pins,i.e. the gate and source sense pins and the dynamic pins, inside oroutside the cover of the housing. For example, where the cover of thehousing comprises ends of a first height carrying the control terminals,and a low profile middle portion forming a recess or trough, the gatedriver board is mounted within the recess or trough of the housing, e.g.within the footprint of the module, and below the height of the busbars.For higher reliability, ceramic decoupling capacitors are provided onthe driver board, i.e. to place the capacitors further away from theheat source. Preferably components of the driver board such asdecoupling capacitors are also low profile.

As an example, the features of this design approach allow for a powermodule comprising multiple paralleled high-speed power switchingdevices, with a gate driver board mounted thereon, to be configured tofit a standard power module form factor, such as a 62 mm module, i.e., arectangular volume 62 mm×106 mm×30 mm in height. The low-profile middleportion allows for shorter, low inductance control terminals which aredirectly connected to control contact areas of the power substrate, toenable, high di/dt switching with reduced gate loop inductance comparedto conventional power module configurations. A power module of anembodiment such as described with reference to FIGS. 7 to 22, andmodifications and variants thereof, which is referred to as a“U-Module”, provides options for a power module comprising paralleledGaN switches, which could be sized to retrofit existing systems, meetingcurrent creepage and clearance standards, while providing improvedperformance, particularly with respect to reduced gate loop inductanceand improved balancing of power commutation loop inductances. It will beappreciated that the specific embodiments are described in detail by wayof example only. Variants and modifications are contemplated forhalf-bridge, full-bridge and other switching topologies using GaN HEMTs.For example, features of the different embodiments may be combined invarious combinations to provide modifications of these embodiments.

Since GaN HEMTs turn on and off on a nanosecond time scale, reducingstray (parasitic) inductances, i.e. to reduce Ldi/dt transients, isimportant to improve or optimize performance. This is particularlyimportant when multiple GaN switches are connected in parallel, anddifferent path lengths of conductive interconnect traces introducedifferent inductances, and resistances, to cause imbalances in each gatedrive loop and each power commutation loop. The design principles forpower modules described herein are intended to reduce these parasitics.It is contemplated that these design principles may also be applicableto power modules for other fast wide-bandgap switching devices, e.g. SiCbased power switching devices.

FIG. 23 shows a photograph of a customized power module comprising a GaNHEMT half-bridge, comprising five HSS/LLS connected in parallel, inwhich the arrangement of the LSS and HSS GaN HEMTs and the configurationof power terminals is similar to that of the low profile power moduleshown in FIG. 3. This type of customized arrangement provides forbalanced power commutation loops for each of the parallel-connectedswitches, as indicated schematically by the red arrows. However,customization of housing modules to optimize performance for eachapplication, e.g. a half-bridge or full-bridge or other arrangement ofGaN HEMTs, add significant design research and development time andcosts, and tooling costs for customized modules are expensive. Powermodules with non-standard dimensions and power terminal arrangementscannot readily be retro-fitted to existing/legacy power systems. Thatis, power modules having customized configurations are expensive tofabricate, and may not be compatible for retro-fitting existing systems.Thus, it is also desirable to provide modifications or improvements toexisting housing type power modules, to meet performance requirementsfor GaN switching devices at lower cost.

Considering design principles applied for the example embodiments of theU-modules describe above, it will now be shown that these designprinciples can be applied for lower-cost modifications of commerciallyavailable housing type power modules for improved dynamic performance.

For example, consider a three-phase inverter having an external packagestructure of a conventional form such as shown in FIG. 24, e.g. anInfineon HybridPACK Drive™ type power module, used for Si-IGBT or SiCswitching devices, where multiple devices are connected in parallel toprovide a required current switching capacity. FIG. 25 shows an exampleof this type of package adapted for use with two paralleled GaN HEMTswitching devices, i.e. HSS1 and LSS1 and HSS2 and LSS2. In this type ofsubstrate layout, as illustrated schematically by the dashed linesindicating the first power commutation loop Loop1 for HSS1 and LSS1 andthe second power commutation loop Loop2 for HSS2 and LSS2, the powercommutation loops are unbalanced, i.e. differ in parameters such as pathlength, inductance, resistance. FIG. 26 shows an enlarged schematic planview to illustrate a conventional arrangement of a substrate andcomponents and connections of one phase of the device structure shown inFIG. 25. This arrangement includes source sense SS pins and gate pins inclose proximity to each LSS and HSS. However, as illustrated in FIG. 25,the arrangement of the power terminals introduces significant circuitparasitic inductance. For paralleling applications, the resultingquasi-common source inductance will cause oscillations.

FIG. 27 shows a module which is modified to add additional pins forpower connections to V+, V− and Vo, i.e. additional “dynamic performancepins” which are configured to provide a lower inductance path whichbalances the power commutation loop for parallel connected switchingdevices, as described with reference to FIGS. 14 and 15A for the powermodule of the first embodiment. The dynamic performance pins 140P and140N to the high side drain and low side source are employed in anexisting power module to redirect the high-frequency current withoutmoving or reconfiguring the power terminals.

As illustrated schematically in FIG. 28, the additional dynamic pinsprovide for balancing of the inductance of the power commutation loop ofeach parallel connected GaN HSS/LSS switch. Addition of an arrangementof dynamic pins for the power buses is feasible as a simple, low-cost,modification to commercially available housing type modules thatsignificantly reduces parasitic inductances in the power commutationloops. Although this design modification does not benefit fromlow-profile, low-inductance terminal members, so that the distancebetween the switching devices and the gate driver board is reduced,adding the dynamic performance pins to reduce the parasitic inductancesin the power commutation loops does help to reduce the mutual inductancebetween the power loop and the gate drive loop.

It will be appreciated that housing type power modules of forms otherthan the HybridPACK Drive module may be similarly modified to adddynamic performance pins to reduce parasitic inductances in the powercommutation loops. The power module may be configured so that the formfactor of the housing, comprising the baseplate and the housing has thegeneral form and geometry of an industry standard module, such as a 62mm rectangular module with mounting holes at each end or at each corner,or any other industry standard form factor of other dimensions, withdynamic performance pins, to redirect high-frequency current. Thedynamic performance pins can be readily implemented, at low cost. Theaddition of dynamic performance pins to existing forms of power modulesprovides for improved performance of parallel connected GaN switchingdevices, without requiring expensive customization and tooling.

Power modules of several embodiments have been described by way ofexample, comprising one or more features that offer improvedperformance, with at least one of reduced stray inductance of the gateloop circuit, and balancing of inductances in the power commutationloops of parallel connected power switching devices, to take advantageof ultra-fast switching capabilities of wide-bandgap semiconductor powerswitching devices, such as GaN HEMTs. Elements of power modules of oneembodiment may be combined with elements of power modules of one or moreof the other embodiments, to provide variants or modifications, or toprovide power modules of alternative form factors. While examples ofpower modules configured for a half-bridge and for a full-bridge switchtopology using GaN E-HEMTs have been described in detail above, it willbe apparent that in other alternative embodiments, the power substratemay be configured for other well-known switch topologies comprisingwide-bandgap semiconductor power switching devices, e.g. SiC or GaNtransistors.

Although embodiments of the invention have been described andillustrated in detail, it is to be clearly understood that the same isby way of illustration and example only and not to be taken by way oflimitation, the scope of the present invention being limited only by theappended claims.

The invention claimed is:
 1. A power module for a wide-bandgapsemiconductor power switching device, comprising: a housing comprising abaseplate and a cover; a power substrate in thermal contact with thebaseplate, a topology of the power substrate being configured formounting thereon of at least one wide-bandgap semiconductor powerswitching device, the power substrate comprising conductive tracksdefining a plurality of power buses and control contact areas for eachpower switching device; a plurality of power terminal members, eachpower terminal member extending from one of the power buses on the powersubstrate, through the cover of the housing, to a power terminal at afirst height h₁ from a base of the baseplate; and a plurality ofterminal members comprising control terminal members extending from eachof the control contact areas on the power substrate to a controlterminal at a second height h₂ from the base, wherein the second heighth₂ is less than the first height h₁.
 2. The power module of claim 1,wherein the first height h₁ is selected to meet required creepage andclearance specifications and the second height h₂ is selected to providelow-profile control terminals for low stray inductance of a gate driveloop for each power switching device.
 3. The power module of claim 1,wherein the control terminals comprise gate and source-sense terminalsfor the gate drive loop of each power switching device, wherein controlcontact areas for the gate and source-sense are located adjacent eachpower switching device and the gate and source-sense terminal membersextend directly from said control contact areas to provide a lowinductance signal path for a gate drive signal.
 4. The power module ofclaim 3, wherein for wide bandgap semiconductor switching devicescomprising GaN E-HEMTs, the gate and source-sense terminals provide saidlow inductance signal path for a gate drive signal having a strayinductance meeting specifications for high di/dt switching transitions,wherein turn-on and turn-off times of the GaN E-HEMTS are in a range of1 ns to 10 ns.
 5. The power module of claim 4, wherein said strayinductance is ≤10 nH.
 6. The power module of claim 2, wherein saidrequired clearance and creepage specifications provide for abusbar-to-heatsink distance for one of: ≥100V operation; 300V to 400Voperation; ≥600V operation; and ≥1200V operation.
 7. The power module ofclaim 1, wherein the cover comprises a first portion and a secondlower-profile portion, the power terminals extending through the firstportion at the first height h₁ and the control terminals extendingthrough the second lower-profile portion at the second height h₂, formounting a gate driver board on the lower-profile portion of thehousing, with the gate driver board connected to the control terminals.8. The power module of claim 1, wherein the cover comprises end portionsand a lower-profile middle portion defining a recess, the powerterminals extending through the end portions of the housing at the firstheight h₁, and the control terminals extending through the lower-profilemiddle portion at the second height h₂, for mounting a gate driver boardin the recess, with the gate driver board connected to the controlterminals.
 9. The power module of claim 1, wherein the topology of thepower substrate is configured for mounting thereon of a plurality ofwide-bandgap semiconductor switching devices connected in parallel, anda plurality of dynamic performance terminal members extending from thepower buses, adjacent each power switching device, for connection to agate driver board, the dynamic performance terminal members having anarrangement that balances inductances of power commutation loops of eachpower switching device and provides a low inductance path for highfrequency current.
 10. The power module of claim 1, comprising at leastone of the following features: wherein the height h₂ provides clearanceabove the power substrate for mounting of power switching devices on thepower substrate, wherein each power switching device comprises apackaged GaN HEMT; wherein height h₁ is ≥14 mm and h₂ is ≤4 mm and theheight difference h₁−h₂ provides clearance for mounting of a gate driverboard on the control terminals; wherein height h₁ is ≥30 mm and h₂ is ≤4mm and the height difference h₁−h₂ provides clearance for mounting of agate driver board on the control terminals; having a generallyrectangular baseplate, having a width and length, wherein the powerterminals are located at each end of the module and the controlterminals are arranged in rows extending lengthwise along a middleportion of the module; wherein the topology of the power substrate isconfigured for mounting thereon of a power switching device comprising asingle wide-bandgap semiconductor power switching device; wherein thetopology of the power substrate is configured for mounting thereon of apower switching device comprising a plurality of wide-bandgapsemiconductor power switching devices; wherein the power substratetopology is configured for a single switch, a half-bridge, afull-bridge, or other switch topology; wherein the power substratetopology is configured for a wide-bandgap semiconductor switching devicecomprising a single switch GaN E-HEMT; wherein the power substratetopology is configured for a wide-bandgap semiconductor switching devicecomprising a plurality of GaN E-HEMTs; wherein the power substratetopology is configured for a wide-bandgap semiconductor switching devicecomprising a GaN E-HEMT half-bridge; and wherein the power substratetopology is configured for a wide-bandgap semiconductor switching devicecomprising a GaN E-HEMT full-bridge.
 11. A power module for wide-bandgapsemiconductor switching device comprising: a housing comprising abaseplate and a cover, the baseplate defining a footprint of generallyrectangular form comprising ends having a width and sides having alength; a power substrate in thermal contact with the baseplate, atopology of the power substrate being configured for mounting thereon ofa plurality of semiconductor power switching devices arranged as firstand second rows extending lengthwise, comprising a first row ofhigh-side device positions and a second row of low-side devicepositions; the power substrate comprising conductive tracks defining aplurality of power buses and a plurality of control contact areas forthe switching devices, wherein the plurality of power buses extendlengthwise adjacent to said first and second rows of high-side andlow-side device positions; first and second rows of control contactareas are arranged adjacent the first and second rows of high-side andlow-side devices positions; a plurality of power terminal members, eachpower terminal member extending from one of the power buses on the powersubstrate, through the cover of the housing to a power terminal at afirst height h₁ from a base of the baseplate; and a plurality of controlterminal members, each control terminal member extending from one of thecontrol contact areas on the power substrate to a control terminal at asecond height h₂ from the base, wherein the second height h₂ is lessthan the first height h₁.
 12. The power module of claim 11, wherein thecontrol terminals comprise gate and source-sense terminals for eachpower switching device, and height h₂ is selected to provide low-profilecontrol terminals for low stray inductance of a gate drive loop for eachpower switching device.
 13. The power module of claim 11, wherein thecontrol contact areas for the gate and source-sense of each powerswitching device are located adjacent each power switching device andthe gate and source-sense terminal members extend directly from saidcontrol contact areas to provide a low inductance signal path for a gatedrive signal.
 14. The power module of claim 11, wherein the height h₂provides clearance above the power substrate for mounting of powerswitching devices on the power substrate, and wherein each of the powerswitching devices comprises packaged GaN HEMT.
 15. The power module ofclaim 11, wherein the first height h₁ is selected to meet requiredclearance and creepage specifications for the power terminals.
 16. Thepower module of claim 11 wherein the first height h₁ is ≥14 mm and thesecond height h₂ is ≤4 mm, the first height h₁ being selected to meetrequired clearance and creepage specifications for the power terminals.17. The power module of claim 11, wherein the cover comprises endportions and a lower-profile middle portion defining a recess, the powerterminals extending through the end portions at the first height h₁ andthe control terminals extending through the lower-profile middle portionat the second height h₂, for mounting of a gate driver board in therecess with the gate driver board connected to the control terminals.18. The power module of claim 11, wherein the topology of the powersubstrate is configured for one of: a single switch, a half-bridge, anda full-bridge.
 19. The power module of claim 11, wherein the power busesand control contact areas configured for a single switch topology, andfurther comprising at least one GaN E-HEMT mounted on the powersubstrate to form the single switch.
 20. The power module of claim 11,wherein the power buses and control contact areas of the power substrateare configured for a single switch topology, and further comprising aplurality of GaN E-HEMTs mounted on the power substrate and connected inparallel to form the single switch.
 21. The power module of claim 11,wherein the power buses and control contact areas of the power substrateare configured for a half-bridge topology, and further comprising aplurality of GaN E-HEMTs mounted in the first row of high-side devicepositions and the second row of low-side device positions, andinterconnected to form the half-bridge.
 22. The power module of claim11, wherein the power buses and control contact areas of the powersubstrate are configured for a full-bridge topology, and furthercomprising a plurality of GaN E-HEMTs mounted in the first row ofhigh-side device positions and the second row of low-side devicepositions and interconnected to form the full-bridge.
 23. The powermodule of claim 11 wherein each switch position comprises a plurality ofsaid GaN E-HEMTs connected in parallel.
 24. An assembly of the powermodule of claim 11 with a gate driver control board comprising gatedriver circuitry for each of the GaN E-HEMTs, wherein the gate drivercontrol board is mounted on the power module and connected to the gateand source-sense control terminals of the power module to form a gatecontrol loop, wherein the gate control loop is configured to provide astray inductance of the gate control loop circuit in a range from 30 nHto less than 5 nH, which meets specifications for operation at aswitching frequency in a range from 10 kHz to 2 MHz.
 25. An assembly ofthe power module of claim 11 with a gate driver control board comprisinga gate driver circuitry for each of the GaN E-HEMTs, wherein the gatedriver control board is mounted on the power module and connected to thegate and source-sense control terminals of the power module to form agate control loop, wherein the gate control loop is configured toprovide a stray inductance of the gate control loop circuit having avalue in a range which meets specifications for high di/dt switchingtransitions wherein turn-on and turn-off times of the GaN E-HEMTS are ina range of 1 ns to 10 ns.
 26. The assembly of claim 25, wherein saidvalue of the stray inductance of the gate control loop circuit is ≤10nH.